<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title></title>
  <script src="../vue.js"></script>
  <style>
    .header {
      font-size: 50px;
      color: red
    }
    .font {
      font-style: italic;
    }
    .deco {
      text-decoration: underline;
    }
  </style>
</head>
<body>
  <div id="root">
    <h1 
      v-bind:class="[{header: isHeader, deco: true}, 'font']"
    >{{title}}</h1>
  </div>
  <script type="module">
    Vue.config.productionTip = false

    var vm = new Vue({
      el: '#root',
      data: {
        title: 'hello',
        isHeader: false
      },

      mounted() {
        setTimeout(() => {
          this.isHeader = true
        }, 3000)
      },
    })
  </script>
</body>
</html>